(1) Field of the Invention
The present invention relates to a technique suitable for use in a mobile communications system using a mobile node which enables simultaneous connection to a plurality of access interfaces (access lines) in, e.g., a mobile communication network using a mobile IP (Internet Protocol) for managing maintenance of communication during movement of a mobile terminal (a mobile node) such as a portable cellular phone, a PDA (Personal Digital Assistant), or the like.
(2) Description of the Related Art
In association with recent proliferation of the Internet, communication using an IP has become widespread. A mobile IP which enables mobile communication using an IP is being contemplated by IETF (Internet Engineering Task Force), and mobile communication using a mobile IP is on its way of becoming feasible. The mobile IP is a technique for rendering communication continuous by having registered, in an HA (Home Agent) serving as a mobility management node, a destination address (CoA: Care of Address) showing the current location of the mobile terminal (MN: Mobile Node) even when the MN has moved.
A communication method using a mobile IP will be described hereinbelow by reference to FIG. 35.
First, the MN is assumed to be in connection with a sub-network (local link) subordinate to an access router (AR1). A destination address (CoA) used by the MN in this case is CoA1. When having moved to a link of the AR1, the MN acquires or generates the destination address CoA1 and registers the destination address in a location information cache (BC: Binding Cache) by use of a location registration message (BU: Binding Update). A CN (Correspondent Node) is a counterpart communication node at the other end, and transmits a packet addressed to a home address (HoA: Home of Address) of the MN.
This packet is delivered to the HA. The HA intercepts the packet, encapsulates the packet with the destination address that is obtained as a result of the location information cache of the HA having been referred to or retrieved, and transmits the thus-encapsulated packet. Since the current destination address of the MN is set to CoA1, the encapsulated packet is delivered to the MN. Upon receipt of the packet, the MN unpacks (decapsulates) the encapsulated packet to thus extract the original packet addressed to the HoA, thereby interpreting that the packet is addressed to the HoA of the MN. In this way, the MN enables receipt of a packet at a location to which the MN has moved.
Next, the MN is assumed to have moved further to a link of another access router (a link of an AR2). Then, the MN generates an address CoA2 used by the location to which the MN has moved (the link of the AR2). The MN again registers the destination address CoA2 in the HA by means of a location registration message. As a result, the destination address of the MN registered in the location information cache of the HA is updated from CoA1 to CoA2.
As in the previously-described case, the CN transmits a packet addressed to the home address (HoA) of the MN. This time, the packet is encapsulated with the destination address CoA2 by the HA, and then transferred. The packet encapsulated with the destination address CoA2 is delivered to the MN, and the MN decapsulates the packet, to thus extract the packet addressed to the HoA of the CN. The reason for this is that, since the current packet is addressed to the same destination as that to which the preceding packet is addressed, a higher-layer application can receive a packet from the CN without becoming aware of movement of the MN even when the MN has moved. In this way, even after having moved, the MN can continue communication with the CN without interruption (without interrupting the application) [such switching of a packet transfer path (access line) is called “handover”].
To date, various access networks have been developed and put into practice. Available access networks include an access network using, for example, a third-generation (hereinafter called a “3G”) mobile communications network, a second-generation (hereinafter called a “2G”) mobile communications network [which is a communication scheme called PDC (Personal Digital Cellular) in Japan or GSM (Global System for Mobile Communications) in Europe], a PHS (Personal Handyphone System), or a wireless LAN (Wireless Local Area Network); or any of various access networks such as an Ethernet (registered trademark) connection employed in businesses, an ADSL (Asymmetric Digital Subscriber Line), or an ISDN (Integrated Services Digital Network). Under these environments, the user can select and use an optimum access network at all times.
For instance, as described in Non-Patent Document 1 provided below, switching is automatically performed so as to be able to connect to an optimum network instantaneously without interrupting communication during usage of a mobile personal computer or the like. When a large-volume attached file is downloaded, high-speed communication, such as wireless LAN, is used. In contrast, a PHS network is used for ordinary communication. Thus, the user can establish communication in the optimum network environment without becoming aware of which one of the networks is in communication with the user.
Techniques described in Patent Documents 1 and 2, which are provided below, are available as another technique of the mobile communications system. A technique described in Patent Document 1 (a multimode general-purpose mobile communications system) is for a case where, in a system into which various mobile communications systems such as satellite mobile communications systems are combined together, a mobile terminal performs handover on the basis of at least one parameter (e.g., cost, capacity, transmission speed, or the degree of usability) in addition to connection quality when determining handover.
As a result, under the technique described in Patent Document 1, the mobile terminal continuously scans an available communications network (circuit switching service, packet switching service, wireless LAN, or the like) during movement. For example, when a communications network available in an area where the mobile terminal is moving offers the same service at lower cost than does the communications network available in the home area during utilization of packet switching data service, connection can be switched to a communications network in the area where the mobile terminal is moving. Information about the cost of service is provided to the mobile terminal by means of, e.g., a common channel.
In contrast, the technique described in Patent Document 2 (a communication setting method and electronic equipment) is for causing a mobile PC (electronic equipment) equipped with radio communication means such as a wireless LAN or Bluetooth (a radio transmission scheme using a 2.4 GHz range) to detect a currently-connectable network (an access point) according to the priority level of a previously-registered radio network setting, and to change connection settings for the detected network [a home/office IP address, mail software settings, network settings of a domestic LAN, or settings of a personally-contracted service provider (ISP)]. As a result, even when a change has arisen in the network environment, switching to a different network environment can be realized by the technique described in Patent Document 2.
Patent Document 1                Published Japanese Translation of PCT Patent Application No. HEI-11-501783        
Patent Document 2                JP-2002-252620A        
Non-Patent Document                “First in Japan! Middle Ware for Automatically Switching to an Optimum Network “Seamlesslink V1.0” newly released” [online], Fujitsu Ltd. Jan. 27, 2003 [retrieved on Apr. 25, 2003], URL:http://pr.fujitsu.com/jp/news/2003/01/27.html.        
However, according to the mobile IP technique, the terminal (MN) always has a single home address (HoA), and only one mobile destination address (CoA) corresponds to the home address. Therefore, selective use of an appropriate one from among a plurality of access lines connected simultaneously to the MN in accordance with a service application, such as http (hyper text transfer protocol), ftp (file transfer protocol), and voip (voice over IP), is impossible.
Specifically, as shown in, e.g., FIG. 36, in a state where the home address HoA and the movement destination address CoA are registered in the HA, the destination of packets addressed to the MN is the home address HoA in any one of the following cases: the case where the MN receives html data by accessing a web (Web) server 100; the case where communication with a CN 200 by means of voip is being established; and the case where a file is downloaded from a file server 300 by means of ftp. The HA encapsulates the packets and transmits the thus-encapsulated packets to only one destination address CoA1 or CoA2 at a single time. Therefore, at a given time the MN can receive the plurality of packets by way of only one access line (can perform a mere uniform handover).
This problem arises similarly under the techniques described in above-described Patent Documents 1 and 2. Specifically, under any of these techniques, the mobile terminal detects a usable (connectable) communications network (access line) in an area to which the mobile terminal has moved, and establishes connection with the detected communications network. However, this connection is also uniformly established for all applications. Eventually, the mobile terminal can inevitably establish communication by way of only one access line at a time. Therefore, even in this case, selective use of an appropriate one from among the plurality of simultaneously-connected access lines in accordance with a service application, such as http, ftp, and voip, is impossible.
The present invention has been conceived in light of the problem set forth and aims at causing a mobile terminal to which a plurality of access lines are simultaneously connected to transfer packets by selecting an optimum access line in accordance with the type (attribute) of a service application (data) to be simultaneously used by the mobile terminal.